1. Field of the Invention
The present invention relates to a battery pack that can determine failure while keeping circuit structure simple without providing a complex circuit for the purpose of determining failure.
2. Description of the Related Art
In a battery pack housing batteries, safety can be improved by controlling current with battery voltage. In particular, for a battery pack with lithium ion batteries, a level of safety is attained by controlling voltages below a set voltage. A battery pack implementing this technique houses a protection circuit that detects battery voltage and controls current based on the detected voltage. Since this type of battery pack can be safely used if the protection circuit operates properly, it has the drawback that it cannot be safely used if the protection circuit fails to operate properly. To prevent this drawback, circuits to determine if the protection circuit operates properly have been disclosed. Circuits to determine battery protection circuit failure are cited in Japanese Patent Application Disclosures 2003-304646, 2004-127663, and 2004-282798.